There is nothing you can do but wait. The news said last night the IRS has something like 35 million backlogged returns (I don't know if that number includes the 13 million returns that need to be reviewed for UEC, or if that is a separate backlog) and there is no way to know when the advance payments will actually start to be sent. The IRS is also begging people not to call them.
The bottom line is that if you qualify for the enhanced child tax credit, it will be added to your refund when you file your 2021 return. The advance payments don't change the amount of credit you are eligible for, they just change when you get paid. There is nothing you can do to increase your chances of receiving the advance payments.
You should not have filed an amended return, it's too late to stop that now and you will just have to wait for the IRS to wade through the backlog and catch up.
